Pneumatic pulsator pumping system with pulsator fluid venting valve

ABSTRACT

A pneumatic pump adapted primarily as a left ventricular heart assist device includes a flexible bladder with a rigid housing. A pneumatic driver applies rhymical pulses between the bladder and the housing to repetitively collapse the bladder and establish a pumping action through the bladder, in conjunction with check valves in the inlet and outlet to the bladder. Between the driver and the pump there is provided a pneumatic pulse limiter which includes a flexible diaphragm isolating the driver from the pump. Pulses from the driver are transmitted to the pump only through the flexible diaphragm and the diaphragm is constrained to move only within established limits. Regardless of the magnitude of the pulse from the driver, the maximum pulse applied to the pump cannot exceed that corresponding to the maximum displacement of the diaphragm. 
     Between successive pulses, the portion of the system between the driver and the flexible diaphragm is depressurized. The rapidity with which depressurization occurs is enhanced by provision of a quick release valve between the driver and the diaphragm.

The invention described herein was made in the course of or under acontract with the U.S. Department of Health, Education and Welfare.

BACKGROUND OF THE INVENTION

Efforts to develop artificial blood pumps have spanned approximately tenyears, including research both in the area of heart assist devices andtotal heart replacement units. One prominent design involves apolyeurathane bladder enclosed in a rigid metal alloy housing. Pneumaticpulses applied between the bladder and the housing produce a pumpingaction through the bladder, in conjunction with check valves at thebladder inlet and outlet ports. Imposition of the pulse expels thecontents of the bladder and termination of the pulse permits the bladderto refill. In a left ventricular assist device, the bladder inlet wouldbe connected to the left ventrical. The ventricular pressure plusresiliancy in the bladder, if any, causes the bladder to refill. Thusthe strength of the heart and the rate at which the pneumatic system isdepressurized between successive pulses determine the rate at which thebladder is filled.

The inside surface of the bladder is flocked with fibers of ablood-compatible polymeric material which promote the formation of astable biological layer along the surface of the bladder. To preservethis layer and to otherwise minimize blood damage, the inside surfacesof the bladder should not be permitted to contact each other duringoperation.

Accordingly, it is an object of this invention to provide a controldevice for controlling the collapse pattern of the flexible bladder in apneumatic blood pump.

Another object of this invention is to promote rapid filling of thebladder during depressurization of the pneumatic system.

SUMMARY OF THE INVENTION

In a pneumatic pump of the type comprising a flexible bladder enclosedin a rigid housing, gas rhythmically injected and released between thebladder and the housing produces the desired pumping action incooperation with one-way valves located at inlet and outlet ports to thepump. A fixed quantity of driving gas combined between the flexiblebladder and the inner wall of the housing constitutes a pneumatic systemwhich, when subjected to a pulse, transmits it to the bladder, expellingfluid therefrom. Between pulses the pneumatic system is depressurized.Compressed gas therein is promptly vented to minimize the time requiredfor depressurization and, accordingly, promote rapid refilling of thebladder.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view illustrating one embodiment of a pneumaticcontrol device constructed in accordance with the present invention;

FIG. 2 illustrates the pneumatic control device of FIG. 1 installed in apneumatically operated blood pump system;

FIG. 3 is a partially cut-away prospective view illustrating analternate embodiment of a pneumatic control device constructed inaccordance with the present invention; and

FIG. 4 is a sectional view of a pneumatic control device constructed inaccordance with the present invention, including the structurerepresented in FIG. 3.

DETAILED DESCRIPTION OF THE DRAWINGS

Referring to FIG. 1, there is disclosed a pneumatic control device 10including a rigid cylindrical housing 12 confining therein a flexiblediaphragm means 14. The diaphragm means 14 includes a flexible sealingmember 16 having a shape complimentary to that of the housing 12 andadapted for rolling contact along the cylindrical walls of the housing.A central portion of the flexible sealing member 16 is provided with apair of stiffeners 18 and 20 on opposite sides thereof. The housing 12consists of an open cylinder 22 and closure 24 held together by anelement 26. The peripheral edge 28 of the diaphragm means 14 is firmlyheld between the cylinder 22 and the closure 24. The housing 12 and thediaphragm means 14 thus define two chambers, 30 and 32, which arepneumatically isolated from each other by the flexible sealing member16.

The pneumatic control device 10 is situated between pneumaticallyactuated pump means 34 and pneumatic driver means 36. From the chamber30 there is provided a port 38 in pneumatic communication with a pumpmeans 34, shown in FIG. 2. The pump means 34 may be more fullyunderstood by reference to co-pending U.S. Pat. application Ser. No.647,842, filed Jan. 9, 1976, for "Pneumatic Blood Pump" in the name ofVictor L. Poirier. The chamber 32 is in pneumatic communication with thepneumatic driver means 36, shown in FIG. 2, through the means 40 forminga passageway. In the embodiment of FIG. 1, the passageway means 40 iscentrally disposed in the cylinder 22 and an inward extension thereofforms a stop means 42 for engagement with the stiffener 20. The openings44 are provided in the stop means 22 so that it does not blockcommunication between the chamber 32 and the passageway means 40. Thedistance between the peripheral edge of the stop means 42 and the innersurface of the end wall 23 establishes the maximum volume of the chamber30. As will hereafter be explained, the maximum volume of the chamber 30determines the maximum stroke of the pump means 34, independently of themagnitude of pneumatic pulses supplied by the driver means 36.

Mounted upon the stiffener 20 and extending through the passageway means40 into a transparent connecting tube 46 is an indicator 48. Theindicator may be calibrated to indicate that position of the diaphragmmeans 14. When in the position of FIG. 1, it provides an indication ofmaximum stroke volume of the pump 34. During operation of the pump 34,the extent of its transilatory movement indicates whether or not thepump is operating on full stroke or partial stroke.

Reference is made to FIG. 2, where the pneumatic control device 10 isshown interposed betwen the pump means 34 and the pneumatic driver means36. The pump means 34 includes a rigid housing 50 containing a flexiblebladder 52 in communication with an inlet conduit 54 and an outletconduit 56. At the locus of communication between the bladder 52 and theconduits 54 and 56 there appears, respectively, inlet valve means 58 andoutlet valve means 60. The inlet valve means 58 and the outlet means 60are both check valves which permit flow only in the direction of arrows62. A port 64 in the housing 50 establishes fluid communication with theport 38 of the pneumatic control device, through the flexible tube 66.Fluid communication between chamber 32 and the pneumatic driver means 36is established through the passageway means 40, the transparentconnecting tube 46, a pneumatic release valve means 68 and a conduit 70.

The pneumatic release valve means 68 includes an elongated chamber 72enclosing a reciprocal member 74. From one end of the chamber 72 a firstport 76 communicates with the conduit 70. From a point in the sidewallof the conduit 70, adjacent the end opposite the first port 76, a secondport 78 communicates with the tube 46. In the end of the elongatedchamber 72 opposite the end forming the first port 76, there is formed athird port 80 in communication with the environment and associated withan inwardly extending tube 82. The pneumatic release valve means isconstructed such that the reciprocal member 74 moves to the solid lineposition, as shown in FIG. 2, to block the port 80 and unblock the port78. In this position fluid communication is established through theelongated chamber 72, between the pneumatic driver means 36 and thechamber 32 of the pneumatic control device 10. When the member 74 blocksthe port 80, the reciprocating member 74 is positioned to locate aperipheral edge thereof immediately adjacent the inlet port 78 so thatany flow from the chamber 32 and the tube 46 into the elongated chamber72 will tend to dislodge the reciprocating member 74 from its blockingposition and move it to its unblocking position, as represented by thebroken line representation. A release valve which may be used in thepresently described embodiment is a Humphrey Super Quick Exhaust Valve,available from Humphrey Products of Kalamazoo, Mich.

The pneumatic driver means 36 applies and releases pneumatic pulses in arhythmical fashion. Upon generation of a positive pressure pulse aboveenvironmental pressure, the reciprocal member 74 advances to block aport 80 and establish communication between the pneumatic driver means36 and the chamber 32. Imposition of the pulse in the chamber 32advances the diaphragm means 14 from the stop means 42 to transmit thepulse to the pump means 34, between the bladder 52 and the housing 50.The pulse transmitted between the bladder and the housing is of amagnitude greater than arterial pressure present in the conduit 56 sothat the bladder 52 will collapse and drive its contents into theconduit 56. Upon termination of the pulse from the driver means 36,pressure in the bladder 52 drops below arterial pressure in the conduit56 and the valve means 60 snaps shut. The maximum stroke of the bladder(i.e. the maximum extent to which the bladder 52 can be collapsed) isdetermined by the volume of the chamber 30. When the diaphragm means 14abuts the end of the housing 12 opposite the stop means 42, the bladder52 cannot be further collapsed regardless of the force of the pulseemanating from the driver means 36.

At termination of the pulse, the pneumatic system which includes thechamber 32 is depressurized by the pneumatic driver means 36. Upondepressurization, initial flow from the chamber 32 to the elongatedchamber 72 drives the reciprocal members 74 from the blocking positionand opens the port 80 to the environment. Opening of the port 80 speedsdepressurization of the pneumatic system which includes the chamber 32and therefore minimizes the time required for refilling of the bladder52, as will hereafter be further explained.

The elongated chamber 72 is situated in the pneumatic system so that,upon depressurization by the driver means 30, the compressed gas in thechamber 32 expands into the elongated chamber 72. The flow resultingtherefrom is augmented by a similar expansion of air in the closedpneumatic system which incorporates the chamber 30 and also by venouspressure in conduit 54. The advantage of the pneumatic release valvemeans 68 is that it speeds depressurization and, as aforesaid, speedsrefilling of the bladder 52. The pneumatic release valve 68 is situatedclosely adjacent to the pneumatic control device 10, thus permittingdepressurization to occur close to the control device. Whendepressurization occurs only through the pneumatic driver means 36, theresistance inherent in the pneumatic system between the chamber 32 andthe driver means 36 acts as a delay.

Reference is now made to FIG. 3 which discloses an alternate embodimentof the pneumatic control device of the present invention. The pneumaticcontrol device of FIG. 3 is similar to that shown in FIG. 1 with thefurther provision that the stop means for limiting movement of thediaphragm means is adjustable. Like numerals are used to designate likeparts.

The stop means 42, to establish limits upon movement of the diaphragmmeans 14, establishes the maximum volume of the chamber 30. Threads 84are provided around the outer surface of the cylindrical housing 12 andmate with corresponding threads 86 of a hood 88. Associated with thehood 88, in a manner to be described hereafter, is a stop element 90adapted to abut the stiffener 20. The passageway means 40 extendscentrally through the stop element 90.

Along the upper periphery of the stop element 90 is attached a spidermeans 92, the arms of which extend through slots 94 in an extension 96formed integrally with and extending outwardly from the end wall 23 ofthe cylinder 22. The extension 96 is configured to reciprocallyconstrain the stop element 90. The spider means 92 is affixed to thehood 88 by a plate 98 having a recessed area 100 adapted to accommodatethe outwardly extended arms of the spider means 92. The plate 98 isaffixed to the inner surface of the hood 88 so that the spider meanslinks the hood 88 to the stop element 90. The surfaces of the hood 88and the plate 98 which contact the outwardly extended arms of the spidermeans 92 may be lubricated, as by being coated withpolytetrafluoroethylene or the like, to minimize friction.

Operation of the stop means 42 will now be described. Counterclockwiserotation of the hood 88 increases displacement of the hood from the endwall 23. Upon such rotation of the hood, the plate 98 rotates withrespect to the spider means 92 and advances the spider means and theattached stop element 90 so that the periphery of the stop elementadapted to engage the diaphragm means 14 approaches the end wall 23 ofthe cylinder 22. Maximum displacement occurs when the peripheral portionof the stop element 90 is coincident with the inner surface of the endwall 23. This condition defines the maximum volume for the chamber 30.Similarly, clockwise rotation of the hood 88 advances the stop elementtoward the closure 24 to reduce the maximum effective volume of thechamber 30. The stop element 90 having been positioned, the apparatus ofFIG. 3 operates as that of FIG. 1. The annular bead 15 surrounding thestiffener 18 serves to avoid contact between the stiffener 18 and theclosure 24 and to cushion the terminal portion of the stroke of thediaphragm means 14. It also insures precise cutoff of fluid flow throughthe port 38.

FIG. 4 is another view illustrating the apparatus of FIG. 3 inconjunction with certain associated equipment. Additionally, the stopmeans 42 is illustrated in the fully retracted position, establishingthe maximum volume of the chamber 30. Like numerals are used todesignate like parts.

The passageway means 40 extends through the stop element 90 andcomprises a connection 102 adapted to receive a conduit 104 forestablishing pneumatic communication with a pneumatic driver means.Teflon rings 106 are interposed between the spider means 92 and the hood88 and between the spider means and the plate 98.

Communicating with the chamber 30 is vent means 108. The vent meanscomprises a line 110, solenoid valve in fluid communication with acontainer 114 holding a desiccant. The container 114 is open to thecanister 116 and ultimately to the environment. In operation of thepreferred embodiment herein described, the chamber 30 is atenvironmental pressure when in maximum volume state. To maintain thiscondition, the chamber 30 is periodically opened to the environment whenthe diaphragm means 14 is fully retracted against the stop means 42,whatever the position of the stop means. The solenoid valve 112 isopened to the environment. Air passing into the chamber 30 from theenvironment travels through the container 114 and is dehydrated bydesiccant contained therein. Desiccant within container 114 may alsoserve to extract moisture from air within the chamber 30 which hascollected there by diffusion through the wall of the bladder 52.

Also in communication with the chamber 30 is a pressure transducer 118for providing a continuous signal proportional to pressure within thechamber. The output from the pressure transducer 118 may be used toprovide an input to a monitoring device of the type described inco-pending U.S. Pat. application Ser. No. 647,841, filed Jan. 9, 1976,for "Pneumatic Pump Monitor" in the name of David Gernes (Docket No.75-35). Further, in substitution of the indicator 48 illustrated inFIGS. 1 and 2, there may be provided a linear voltage displacementtransducer 120 connected to the stiffener 20 through a means 122. Thetransducer 120 provides a voltage proportional to position of thediaphragm means, thereby providing an electrical signal analogous to thevisual signal described in connection with the embodiment of FIGS. 1 and2. As with the pressure transducer 118, the linear voltage transducer120 is adapted to provide an input to a pump monitor as may be morefully understood by reference to the aforesaid co-pending U.S. Pat.application Ser. No. 647,841.

The present invention has been described with reference to variouspreferred embodiments. It should be understood, however, modificationsmay be made by those skilled in the art without departing from the scopeof the invention.

I claim:
 1. A blood circulatory assist device comprising:flexiblebladder enclosed in a rigid housing and defining inlet means and outletmeans for intermittently admitting and releasing blood to and frombladder; means forming a pneumatic system, including as a part thereofthe space between said bladder and said housing; pneumatic pulsegenerator means for rhythmically pressurizing and pressure relievingsaid pneumatic system to rhythmically compress and release said flexiblebladder; means dividing said pneumatic system interposed between saidpneumatic generator and said circulatory assist device for transmittingpneumatic forces from one division of said pneumatic system to theother; and release valve means in said pneumatic system for venting saidpneumatic system between said dividing means and said pneumaticgenerator in response to pressure relief by said pneumatic generator. 2.A blood circulatory assist device comprising:a flexible bladder enclosedin a rigid housing and defining inlet means and outlet means forintermittently admitting and releasing blood to and from said bladder;means forming a closed pneumatic system, including as a part thereof thespace between said bladder and said housing, for transmitting pulsesimparted thereto between said bladder and said housing; means forming asecond pneumatic system pneumatically sealed from said closed pneumaticsystem, said second system being in physical communication with saidclosed system for transferring pneumatic pulses to said closed pneumaticsystem; pneumatic pulse generator means for rhythmically pressurizingand pressure relieving said second pneumatic system for transmittingrhythmical pneumatic pulses to said first pneumatic system and therebyrhythmically compressing and releasing said flexible bladder; andrelease valve means in said second pneumatic system proximate to saidclosed system for venting said second pneumatic system in response topressure relief by said pneumatic generator.